The present invention relates to a method for extracting and purifying stereoisomers from biomass. The present invention also relates to a method for extracting and purifying L-arabinose from sugar beet pulp.
Drug and fine chemical feed stocks have been produced to exacting physical and chemical purity standards or chirality. However, little regard has been given to optical purity. Achieving optical purity requires identifying feed stock components that have stereoisomers and selecting D- or L-forms of chemicals that have stereoisomers. The D- and L-forms are known as stereoisomer pairs, i.e. right and left handed pairs. Stereoisomers are molecules that are identical in atomic constitution, and that have, in some instances essentially identical physical and chemical properties. The stereoisomeric pairs differ in three dimensional arrangement of atoms, optical rotation, and chemical properties.
One type of stereoisomer pair is an enantiomer. An enantiomer is a stereoisomer pair with at least one asymmetric center. Individual stereoisomers of an enantiomer are mirror images of each other. Drugs tend to have enantiomers that have activity which is biologically distinguishable. In some instances, individual enantiomers of drugs have distinguishable biological activity. Naturally occurring, optically impure, or racemic mixtures of stereoisomers have been used as feed stocks in the pharmaceutical and fine chemical industries. In many instances, the quality of the final product has been insensitive to the optical purity of the feedstock. However, in some cases, the chemical and optical purity of the final product has depended, in part, upon the optical purity of the feed stock.
One stereoisomeric drug having one enantiomer which shows a different biological activity in humans than the other enantiomer is d,l-propranolol. l-propranolol acts as a beta-blocker. d-propranolol lacks such activity.
In some instances, one of the enantiomers is toxic while the other enantiomer is benign. For instance, when a d-isomer was removed from d,l-carnitine in a drug composition, doctors could no longer observe symptoms of myasthenia gravis. Symptoms had been observed, however, in patients taking the racemic mixture of d,l carnitine.
One other example is thalidomide. It is well known that ingestion of R,S-thalidomide in the 1950""s by pregnant women led to the birth of children with phocomelia and other embryopathies. It was subsequently found that the R enantiomer of thalidomide is teratogenic and toxic in an animal model while the S enantiomer of thalidomide is neither teratogenic nor toxic in that model. Unfortunately, no benefit is found in humans of using the S enantiomer of thalidomide over the R enantiomer because humans morph the pure S form to a racemic mixture of R,S-thalidomide. It is still unknown which enantiomer of thalidomide is toxic in humans. Therefore, thalidomide use is prohibited in most cases in the United States.
Because enantiomers have radically different biological activity, the FDA has developed a set of rules governing the development of stereoisomeric drugs. These rules can be found at the FDA website. Specifically, the FDA requires that the enantiomeric composition of a drug should be known. That is, the stereochemical identity, strength, quality, and purity should be known in the final product. The FDA has further stated that xe2x80x9cappropriate manufacturing and control procedures should be used to assure stereoisomeric composition of a product, with respect to identity, strength, quality and purity.xe2x80x9d Thus, pharmaceutical feedstocks, and fine chemical feedstocks used to formulate products which come under the FDA regulatory power, must be produced with utmost concern for the chirality of the molecules.
One group of chemicals that is rich in stereoisomers is the group comprising carbohydrates. Conventional carbohydrate chemistry for extracting sugars from sugar cane pulp, bagasse, or sugar beet biomass requires using large amounts of caustic and hydrochloric acid to hydrolyze the cellulose and hemicellulose polymer backbone. In the extraction, the mixed carbohydrate biomass is initially placed into a caustic solution where it forms ellipsoidal aggregates. The typical formulation calls for approximately 100 pounds of caustic for each pound of hemicellulose/cellulose carbohydrate mixture. This extraction step is accompanied by disposal problems. Since the ellipsoidal aggregates are only weakly permeable to aqueous solutions, the hydrolysis process must be performed at high temperatures and for an extended period of time.
What occurs is thermal degradation of the exterior of the ellipsoidal aggregate before the hydrolysis reaction has traversed the radius of the aggregate. The degradation results in a diminished yield and a need to separate the degraded carbohydrate from the hydrolyzed hemicellulose/cellulose mixture. Conventional extraction requires a significant destruction of raw material due to thermal decomposition of the carbohydrate and environmental damage resulting from disposal of caustic and acidic process chemicals.
One embodiment of the present invention includes a process for extracting a stereoisomer from biomass. The process includes providing biomass and subjecting the biomass to instantaneous pressurization and depressurization in a manner effective to separate lignin, hemicellulose and cellulose in the biomass. The process also includes hydrolyzing the hemicellulose to form hemicellulose hydrolysates. One or more stereoisomers is separated from the hemicellulose hydrolysates using chromatography.
Another embodiment of the present invention includes a system for obtaining monosaccharides, oligosaccharides and polysaccharides from biomass. The system comprises a mechanism for substantially pressurizing and depressurizing biomass to separate the biomass into hemicellulose, cellulose and lignin. The system also includes a heater for heating the hemicellulose. The system further includes a reactor/mixer for mixing sodium hydroxide with hemicellulose and for making hemicellulose hydrolysates. The system additionally includes a mechanism for selectively separating a hemicellulose hydrolysate based upon the component""s exact sterisomeric identity.
One other embodiment of the present invention includes a process for extracting L-arabinose from sugar beet pulp. The process comprises providing sugar beet pulp and subjecting the sugar beet pulp to substantially instantaneous pressurization and depressurization in a manner effective to separate lignin, hemicellulose and cellulose in the beet pulp. The process also includes hydrolyzing the hemicellulose to form hemicellulose hydrolysates. L-arabinose is separated from the hemicellulose hydrolysates using chromatography.